After filtration, the residue was washed with hot distilled water at 60°C for three times. The crude chitosan (4.1g) was obtained by drying in an air oven at 50°C overnight. One gram of crude chitosan was added into 20 ml of 2% (w/w) acetic acid in a water-bath shaker. The conditions were set as follows: H2O2 level (4%), time (4 h) and temperature (60°C). After reaction, 10% NaOH was used to adjust the solution to neutrality. The residue was removed by filtration, while twofold volumes of ethanol were added to the filtrate. The crystal of water-soluble chitosan was liberated after incubation at ambient condition overnight and dried in an air oven at 50°C. The recovery (%) was calculated as (the weight of water-soluble chitosan/the weight of crude chitosan) ×100.